Back on the OT:
What troubles me about the issue of sexual reproduction is this:
a) It appears to be general consensus that the earliest life forms reproduced by means of asexual replication. This is an integral copy of the original that copies itself and then separates. It's a simple, elegant and effective method.
b) It appears to be the general consensus that sexual reproduction appears in a much later stage of life.
The problem is, how did some organisms evolved from asexual to sexual reproduction? Because it's not a simple variation of the asexual method. It's a much more complex process that requires an enormous level of complexity at the very beginning (not saying that asexual reproduction isn't complex; but sexual reproduction is immensely MORE complex; it's a huge leap forward from asexual reproduction.)
For starters it requires that two separate organisms develop specialized, yet necessarily complementary genetic material, cut by half, that will be recombined by means of sexual activity. This is a gargantuan conceptual difference from asexual replication and can only work with a high level of complexity to start with.